Geologists Find Evidence That North American Glacial Advances Coincided With Iceberg Calving Events

October 26, 1998

Three big events. One big question: How do the major events of the last Ice Ages fit together?

Between 30,000 and 10,000 years ago, the Laurentide Ice Sheet surged over the North American continent numerous times. During that same time period, there were repeated episodes of massive iceberg calving over the North Atlantic, and ice cores from Greenland demonstrate repeated cycles of global warming and cooling.

University of Cincinnati geologist Thomas Lowell will provide one piece of the puzzle by reporting that the ice sheet advances over land marched in step with the iceberg calving events over the ocean Monday, Oct. 26 during the annual meeting of the Geological Society of America in Toronto.

Lowell will provide data from seven different advances of the Great Lakes lobes of the Laurentide Ice Sheet from 10,025 to 26,000 years ago. In each case, Lowell's data indicates that the advances over land coincide with reported events of iceberg calving.

Lowell's data set covers glacial advances from sites in Ohio, Indiana, Michigan, Iowa, and Illinois. "Different parts of the ice sheet are all doing the same thing," noted Lowell.

To insure the quality of their records, Lowell uses a brute force method. "Once we find sites with good context, we hammer them; dating them again and again. We need to replicate our dates to reduce the error bars to make comparisons of events separated by only a few hundred years."

Linking the third piece of the puzzle, climate change, requires yet another comparison this time with the Greenland ice core record. Others have argued that the iceberg calving disrupted ocean circulation patterns and thereby forcing global climate change.

Lowell disagrees. His results indicate that the ice sheet advances occurred toward the end of the recorded cooling periods. This would indicate that the glacial advances were an effect of global cooling, not the actual cause of the climate change. "To be the instigator, the IRDs would have to have happened first." Instead, Lowell concludes both the land and sea events appear to be responding to global cooling and reinforcing the pattern, rather than initiating the change.

Unfortunately, that leaves with Lowell and other scientists with yet another big question: What did cause Earth's climate to cool down?

Lowell's attempt to answer that question took him to southern Chile and the southern Alps of New Zealand earlier this year. That data is still being analyzed.

University of Cincinnati

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